{"id":"CVE-2026-115269","state":"PUBLISHED","title":"HTTP/2 WINDOW_UPDATE and SETTINGS frames reset the request body read timeout in Bandit","description":"Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 request body reader of mtrudel bandit allows an unauthenticated remote attacker to hold stream processes open indefinitely via WINDOW_UPDATE or empty SETTINGS frames sent while a Plug reads the request body.\n\nBandit.HTTP2.Stream.do_read_data/4 in lib/bandit/http2/stream.ex waits for each frame with a fresh read_timeout. A stream WINDOW_UPDATE, or the zero-delta window update that every empty SETTINGS frame delivers to all streams, ends the wait without delivering any body data, and the loop starts a new full countdown. A client that sends one of these 9-byte frames before each countdown expires keeps read_body blocked, together with the stream process and whatever the application holds while reading, for as long as it likes.\n\nThis issue affects bandit: from 1.4.0 before 1.14.0.","publishedAt":"2026-10-26T13:30:24.621Z","updatedAt":"2026-10-26T15:35:52.079Z","severity":{"score":8.7,"label":"High","version":"4.0","vector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","source":"EEF"},"assigner":"EEF","products":["mtrudel bandit"],"affected":[{"vendor":"mtrudel","product":"bandit","packageName":"bandit","packageURL":"pkg:hex/bandit","defaultStatus":"unaffected","versions":[{"version":"1.4.0","status":"affected","lessThan":"1.14.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"repo":"https://github.com/mtrudel/bandit"},{"vendor":"mtrudel","product":"bandit","packageName":"mtrudel/bandit","packageURL":"pkg:github/mtrudel/bandit","defaultStatus":"unaffected","versions":[{"version":"fff06efe3be962b484bd4d3eb339372fda5a231f","status":"affected","lessThan":"220b9dfd27f9a21305be2afc75cbe585ddc24e7a","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"repo":"https://github.com/mtrudel/bandit"}],"references":["https://github.com/mtrudel/bandit/security/advisories/GHSA-p2qv-vx88-385x","https://cna.erlef.org/cves/CVE-2026-115269.html","https://osv.dev/vulnerability/EEF-CVE-2026-115269","https://github.com/mtrudel/bandit/commit/fff06efe3be962b484bd4d3eb339372fda5a231f","https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a"],"weaknesses":["CWE-835","CWE-770"],"ingestedAt":"2026-10-29T20:10:43.281Z","source":{"repository":"CVEProject/cvelistV5","path":"cves/2026/115xxx/CVE-2026-115269.json","commit":"556c9d3a8cd17e218bb8e452ba7cd619a384ff47"},"raw":{"dataType":"CVE_RECORD","dataVersion":"5.2","cveMetadata":{"cveId":"CVE-2026-115269","state":"PUBLISHED","datePublished":"2026-10-26T13:30:24.621Z","dateUpdated":"2026-10-26T15:35:52.079Z","assignerShortName":"EEF","assignerOrgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateReserved":"2026-10-23T10:15:01.872Z"},"containers":{"cna":{"title":"HTTP/2 WINDOW_UPDATE and SETTINGS frames reset the request body read timeout in Bandit","descriptions":[{"lang":"en","value":"Allocation of Resources Without Limits or Throttling vulnerability in the HTTP/2 request body reader of mtrudel bandit allows an unauthenticated remote attacker to hold stream processes open indefinitely via WINDOW_UPDATE or empty SETTINGS frames sent while a Plug reads the request body.\n\nBandit.HTTP2.Stream.do_read_data/4 in lib/bandit/http2/stream.ex waits for each frame with a fresh read_timeout. A stream WINDOW_UPDATE, or the zero-delta window update that every empty SETTINGS frame delivers to all streams, ends the wait without delivering any body data, and the loop starts a new full countdown. A client that sends one of these 9-byte frames before each countdown expires keeps read_body blocked, together with the stream process and whatever the application holds while reading, for as long as it likes.\n\nThis issue affects bandit: from 1.4.0 before 1.14.0."}],"affected":[{"vendor":"mtrudel","product":"bandit","packageName":"bandit","packageURL":"pkg:hex/bandit","defaultStatus":"unaffected","versions":[{"version":"1.4.0","status":"affected","lessThan":"1.14.0","versionType":"semver"}],"collectionURL":"https://repo.hex.pm","cpes":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"repo":"https://github.com/mtrudel/bandit"},{"vendor":"mtrudel","product":"bandit","packageName":"mtrudel/bandit","packageURL":"pkg:github/mtrudel/bandit","defaultStatus":"unaffected","versions":[{"version":"fff06efe3be962b484bd4d3eb339372fda5a231f","status":"affected","lessThan":"220b9dfd27f9a21305be2afc75cbe585ddc24e7a","versionType":"git"}],"collectionURL":"https://github.com","cpes":["cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*"],"repo":"https://github.com/mtrudel/bandit"}],"references":[{"url":"https://github.com/mtrudel/bandit/security/advisories/GHSA-p2qv-vx88-385x","name":"HTTP/2 WINDOW_UPDATE and SETTINGS frames reset the request body read timeout in Bandit","tags":["vendor-advisory","related"]},{"url":"https://cna.erlef.org/cves/CVE-2026-115269.html","name":"EEF CNA record for CVE-2026-115269","tags":["related"]},{"url":"https://osv.dev/vulnerability/EEF-CVE-2026-115269","name":"OSV record EEF-CVE-2026-115269","tags":["related"]},{"url":"https://github.com/mtrudel/bandit/commit/fff06efe3be962b484bd4d3eb339372fda5a231f","name":"Introducing commit fff06ef in mtrudel/bandit","tags":["related"]},{"url":"https://github.com/mtrudel/bandit/commit/220b9dfd27f9a21305be2afc75cbe585ddc24e7a","name":"Fix commit 220b9df in mtrudel/bandit","tags":["patch"]}],"metrics":[{"cvssV4_0":{"Automatable":"NOT_DEFINED","Recovery":"NOT_DEFINED","Safety":"NOT_DEFINED","attackComplexity":"LOW","attackRequirements":"NONE","attackVector":"NETWORK","baseScore":8.7,"baseSeverity":"HIGH","privilegesRequired":"NONE","providerUrgency":"NOT_DEFINED","subAvailabilityImpact":"NONE","subConfidentialityImpact":"NONE","subIntegrityImpact":"NONE","userInteraction":"NONE","valueDensity":"NOT_DEFINED","vectorString":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N","version":"4.0","vulnAvailabilityImpact":"HIGH","vulnConfidentialityImpact":"NONE","vulnIntegrityImpact":"NONE","vulnerabilityResponseEffort":"NOT_DEFINED"},"format":"CVSS","scenarios":[{"lang":"en","value":"GENERAL"}]}],"problemTypes":[{"descriptions":[{"cweId":"CWE-835","description":"CWE-835 Loop with Unreachable Exit Condition ('Infinite Loop')","lang":"en","type":"CWE"}]},{"descriptions":[{"cweId":"CWE-770","description":"CWE-770 Allocation of Resources Without Limits or Throttling","lang":"en","type":"CWE"}]}],"providerMetadata":{"shortName":"EEF","orgId":"6b3ad84c-e1a6-4bf7-a703-f496b71e49db","dateUpdated":"2026-10-26T13:30:24.621Z"},"cpeApplicability":[{"nodes":[{"cpeMatch":[{"criteria":"cpe:2.3:a:mtrudel:bandit:*:*:*:*:*:*:*:*","versionEndExcluding":"1.14.0","versionStartIncluding":"1.4.0","vulnerable":true}],"negate":false,"operator":"OR"}],"operator":"AND"}],"credits":[{"lang":"en","type":"analyst","value":"Peter Ullrich"},{"lang":"en","type":"reporter","value":"Daniel Coles"},{"lang":"en","type":"remediation developer","value":"Mat Trudel"},{"lang":"en","type":"analyst","value":"Jonatan Männchen / EEF"}],"dateAssigned":"2026-10-23T13:25:29.000Z","impacts":[{"capecId":"CAPEC-469","descriptions":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

An unauthenticated client can keep a Bandit HTTP/2 stream, and whatever its request handler holds while reading the body, occupied indefinitely for 9 bytes per read_timeout, and repeat this across many streams and connections. This affects any Bandit server with HTTP/2 enabled whose routes read request bodies, which Plug.Parsers does for POST, PUT and PATCH.

"},{"base64":false,"type":"text/markdown","value":"An unauthenticated client can keep a Bandit HTTP/2 stream, and whatever its request handler holds while reading the body, occupied indefinitely for 9 bytes per `read_timeout`, and repeat this across many streams and connections. This affects any Bandit server with HTTP/2 enabled whose routes read request bodies, which `Plug.Parsers` does for POST, PUT and PATCH."}],"value":"An unauthenticated client can keep a Bandit HTTP/2 stream, and whatever its request handler holds while reading the body, occupied indefinitely for 9 bytes per read_timeout, and repeat this across many streams and connections. This affects any Bandit server with HTTP/2 enabled whose routes read request bodies, which Plug.Parsers does for POST, PUT and PATCH."}]}],"source":{"discovery":"UNKNOWN"},"workarounds":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

Disable HTTP/2 with http_2_options: [enabled: false], so that the vulnerable read path never runs.

"},{"base64":false,"type":"text/markdown","value":"Disable HTTP/2 with `http_2_options: [enabled: false]`, so that the vulnerable read path never runs."}],"value":"Disable HTTP/2 with http_2_options: [enabled: false], so that the vulnerable read path never runs."}],"x_proofOfConcept":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"
    \n
  1. Run Bandit with a Plug that calls Plug.Conn.read_body/2.
    2. \n
  2. Open an HTTP/2 connection and send HEADERS for POST / on stream 1 without END_STREAM.
    3. \n
  3. Every 10 seconds, send a WINDOW_UPDATE on stream 1 with an increment of 1.
    4. \n
  4. The stream stays open for 120 s, eight times the default 15 s read_timeout. Without the WINDOW_UPDATE frames, the server ends the read after about 15 s.
    5. \n
"},{"base64":false,"type":"text/markdown","value":"1. Run Bandit with a Plug that calls `Plug.Conn.read_body/2`.\n2. Open an HTTP/2 connection and send HEADERS for `POST /` on stream 1 without END_STREAM.\n3. Every 10 seconds, send a WINDOW_UPDATE on stream 1 with an increment of 1.\n4. The stream stays open for 120 s, eight times the default 15 s `read_timeout`. Without the WINDOW_UPDATE frames, the server ends the read after about 15 s."}],"value":"* Run Bandit with a Plug that calls Plug.Conn.read_body/2.\n* Open an HTTP/2 connection and send HEADERS for POST / on stream 1 without END_STREAM.\n* Every 10 seconds, send a WINDOW_UPDATE on stream 1 with an increment of 1.\n* The stream stays open for 120 s, eight times the default 15 s read_timeout. Without the WINDOW_UPDATE frames, the server ends the read after about 15 s."}],"x_technicalAnalysis":[{"lang":"en","supportingMedia":[{"base64":false,"type":"text/html","value":"

1. Per-receive timeout. Bandit.HTTP2.Stream.read_data/2 passes a flat read_timeout (default 15,000 ms) to do_read_data/4, which blocks in do_recv/2's receive ... after timeout.

\n

2. Non-progress frames end the wait. A stream WINDOW_UPDATE, delivered through Bandit.HTTP2.Connection.handle_frame/3, or an empty SETTINGS frame, which delivers a zero-delta window update to every stream, is matched inside that receive. do_recv_send_window_update/2 returns a bare %Stream{}, and do_read_data/4 recurses with the identical timeout, restarting the countdown.

\n

3. Nothing else bounds the read. The transport read timeout fires only when no bytes arrive, max_bytes is decremented only by DATA frames, and neither WINDOW_UPDATE nor SETTINGS frames are rate limited. The send path in do_send_data/4 uses a progress-based deadline; the read path does not.

"},{"base64":false,"type":"text/markdown","value":"**1. Per-receive timeout.** `Bandit.HTTP2.Stream.read_data/2` passes a flat `read_timeout` (default 15,000 ms) to `do_read_data/4`, which blocks in `do_recv/2`'s `receive ... after timeout`.\n\n**2. Non-progress frames end the wait.** A stream WINDOW_UPDATE, delivered through `Bandit.HTTP2.Connection.handle_frame/3`, or an empty SETTINGS frame, which delivers a zero-delta window update to every stream, is matched inside that `receive`. `do_recv_send_window_update/2` returns a bare `%Stream{}`, and `do_read_data/4` recurses with the identical `timeout`, restarting the countdown.\n\n**3. Nothing else bounds the read.** The transport read timeout fires only when no bytes arrive, `max_bytes` is decremented only by DATA frames, and neither WINDOW_UPDATE nor SETTINGS frames are rate limited. The send path in `do_send_data/4` uses a progress-based deadline; the read path does not."}],"value":"1. Per-receive timeout. Bandit.HTTP2.Stream.read_data/2 passes a flat read_timeout (default 15,000 ms) to do_read_data/4, which blocks in do_recv/2's receive ... after timeout.\n\n2. Non-progress frames end the wait. A stream WINDOW_UPDATE, delivered through Bandit.HTTP2.Connection.handle_frame/3, or an empty SETTINGS frame, which delivers a zero-delta window update to every stream, is matched inside that receive. do_recv_send_window_update/2 returns a bare %Stream{}, and do_read_data/4 recurses with the identical timeout, restarting the countdown.\n\n3. Nothing else bounds the read. The transport read timeout fires only when no bytes arrive, max_bytes is decremented only by DATA frames, and neither WINDOW_UPDATE nor SETTINGS frames are rate limited. The send path in do_send_data/4 uses a progress-based deadline; the read path does not."}]},"adp":[{"title":"CISA ADP Vulnrichment","metrics":[{"other":{"type":"ssvc","content":{"id":"CVE-2026-115269","role":"CISA Coordinator","options":[{"Exploitation":"none"},{"Automatable":"yes"},{"Technical Impact":"partial"}],"version":"2.0.3","timestamp":"2026-10-26T15:02:19.174445Z"}}}],"providerMetadata":{"shortName":"CISA-ADP","orgId":"134c704f-9b21-4f2e-91b3-4a467353bcc0","dateUpdated":"2026-10-26T15:35:52.079Z"}}]}}}